SP-4302 Adventures in Research: A History of Ames Research Center 1940-1965

 

PART II : A NEW WORLD OF SPEED : 1946-1958

1958

 

16

Research

 

PATTERN

 

[287] WHILE the thinking of the Ames staff was markedly altered by the foreknowledge of NACA's new responsibilities in space research, the inertia of the Laboratory's ongoing research program was such that the program continued largely unchanged during 1958. The inertia was somewhat less in the theoretical than in the experimental field with the result that a few analytical studies of spacecraft trajectories were completed during this period. On the whole, however, 1958 was not a period of high research productivity at Ames. There appeared to be several reasons for this. One was that the research leaders at the Laboratory were devoting time to the planning of future space-age operations. Another was that the staff gave more than the usual attention to the inspection and the Technical Conference that were held during 1958. A third factor was the hovering shadow of impending changes in NACA. Not only did this cause a general psychological disturbance at the Laboratory but it may also have been an important influence in the tendering of resignations by a number of the Laboratory's high-ranking research men.

 

BASIC CONFIGURATIONS AND AIRFLOWS

 

Investigation of arrowhead-wing configurations continued during 1958. An experimental study made by Leland Jorgenson was reported in Memo 4-27-59A,' and another, carried out in the 8- by 7-foot leg of the Unitary Plan facility, was described in TM X-22 1 by Edward Hopkins, Don Jillie and Alan Levin. Further studies were also made of hypersonic configurations designed by the interference method. One of these was reported in RM A58G17, "Aerodynamic Performance and Static Stability of Flat-Top Hypersonic Gliders," by Clarence A. Syvertson, Hermilo R. Gloria, and [288] Michael F. Sarabia. Another program, in which two optimized configurations designed for M = 5 were investigated, was described by David Dennis and Richard Petersen in Memo 1-8-59A. And inasmuch as even hypersonic airplanes must land, it was considered necessary to investigate the slow-speed characteristics of some of the more promising hypersonic configurations. This work, reported in RM A58F03 by Mark Kelly, was carried out in the 40- by 80-foot tunnel.

The canard program, which had earlier received so much attention in the 6- by 6-foot tunnel, was extended during 1958 through the work of John Boyd and Gene Menees, reported in Memo 4-21-59A. Also extended, but in a small way, was the work on boundary-layer control (BLC) which had reached a peak during the previous period in the 40- by 80-foot tunnel. This activity was carried on by Roy Griffin, Curt Holzhauser, and Jim Weiberg. Ames engineers drew considerable satisfaction from the fact that the BLC ideas which they had researched were now being applied to several new fighter aircraft.

The Area Rule was still under investigation in 1958, but as a research subject had about been exhausted. Lionel Levy and Kenneth Yoshikawa produced a simplified numerical method for calculating wave drag using Area Rule principles, and George Holdaway together with Jack Mellenthin and Elaine Hatfield made an experimental investigation, in the 14-foot tunnel, of an interesting blended diamond configuration. The latter work is reported in TM X-105.

During 1958, John Spreiter's extensive work in the field of transonic aerodynamic theory reached a culmination, and end, in a paper (ref. B-60) entitled "Aerodynamics of Wings and Bodies at Transonic Speeds." John presented the paper at the Eighth Japanese National Congress for Theoretical and Applied Mechanics held in Tokyo in September 1958.

 

INLETS

 

Work on air inlets, particularly internal compression inlets, continued at Ames during this period. One such study, concerned with the ever-present and ever-troublesome problem of dealing with the boundary layer, was described in Memo 2-19-59A by Frank Pfyl and Earl Watson. This report covered tests made in the 6- by 6-foot, the 8- by 7-foot, and the 8-by 8-inch tunnels. Additional inlet studies, most of them carried out in Unitary Plan facilities, were made by a number of Ames engineers including Norman Martin, John Gawienowski, Norman Sorenson, Edward Perkins, and Warren Anderson.

 

STABILITY

 

The X-15 research airplane was of fairly unusual configuration and was designed to operate in the outer fringes of the atmosphere where aerody- [289] -namic forces were low. The stability and controllability characteristics of the airplane under these conditions of flight were of very great interest to the designers and prospective operators of the craft. Numerous research programs were undertaken at Ames to establish the operational characteristics of the airplane, and a number of these had to do with measurements of its static and dynamic stability. In the dynamic-stability phase of this work, the test technique developed by Ben Beam (TR 1258) was particularly useful. One study of the static and dynamic rotary stability characteristics of the X-15 was made in the 12-foot tunnel and reported in RM A58F09 by Armando Lopez and Bruce Tinling. Similar studies, but at supersonic speeds, were made in the Unitary Plan facility by two teams comprising, in one case, Ben Beam and Kenneth Endicott and, in the other case, Jack Tunnell and Eldon Latham.

In addition to the studies just mentioned, a couple of quite comprehensive analyses were made of the numerous factors affecting the static stability of airplanes representing advanced types. Covered in the analysis was the rather extreme range of conditions which such airplanes are expected to encounter. These studies were made by George Kaattari and Fred Goodwin and were reported in Memo 12-1-58A and Memo 12-2-58A.

 

FLIGHT RESEARCH

 

Simulators. Increasing interest was now being taken at Ames in ground-based flight simulators. It was beginning to appear that many of the stability and control characteristics of manned aircraft and perhaps of spacecraft could be evaluated more quickly and cheaply, as well as more safely, with ground-based flight simulators. Before such a program was gone into too deeply, however, it was necessary to determine the adequacy of flight simulators by comparing their results with those obtained in flight. And inasmuch as all of the flight conditions could not feasibly be represented in a simulator, it was essential to determine which conditions could safely be disregarded. Many of the flight simulator studies so far undertaken at Ames dealt with these problems.

Typically, the elements of a flight simulator consisted of (1) a cockpit with control stick and flight instruments and/or special visual display; (2) an analog computer to compute both the response of the airplane to control motions and other input factors, and to transmit the information to the instrument display; and (3) a pilot to operate the controls in response to cues offered by the instrument display or in accordance with some other prearranged plan. The cues used by a pilot in the guidance of an actual airplane come from three principal sources: the instruments on the control panel, the motion and attitude of the airplane, and the view of the sky horizon and terrain as seen through the windows of the airplane. In a simulator the instrument display could be provided rather easily, but the simulation of air [290] plane motion and external view could be achieved only at great cost and with much difficulty.

The question of the necessity for simulating airplane motion was of the greatest interest to Ames engineers. There were to be considered six degrees of motion: angular motion about the three (pitch, roll, and yaw) axes, and translational motion along each axis. Of these, angular motions could most readily be simulated; the simulation of translational motions would, however, be difficult. A peculiarly representative combination of angular and translational motions could, it was realized, be obtained by mounting the simulated cockpit on a centrifuge; and Langley, using the Navy's large centrifuge at Johnsville, Pa., had exploited this technique in studies of the X-15.

Langley's work with the Johnsville centrifuge generated a determination in Harry Goett to build moving flight simulators at Ames. In the first such simulator built at Ames, the simulated cockpit was mounted on two motor-driven axes providing a certain amount of angular motion in pitch and roll. This device, called the "pitch-roll chair," was relatively crude; but as 1958 ended, Harry Goett and his staff were laying plans for more sophisticated moving flight simulators.

Of the Ames reports that defined the need and requirements of flight simulators and established their usefulness, three could be taken as representative of this period. First was Memo 10-1-58A by Mel Sadoff, which showed that, except in certain operational ranges, the control system characteristics of airplanes could quite successfully be pilot-evaluated in a fixed flight simulator. Second, there was Memo 1-29-59A, "A Pilot Opinion Study of Lateral Control Requirements for Fighter-Type Aircraft," by Brent Y. Creer, John D. Stewart, Robert B. Merrick, and Fred J. Drinkwater III. This report described one of the early uses of the pitch-roll chair and provided a comparative evaluation of the lateral-control requirements of fighter aircraft as determined in actual flight and through the use of flight simulators of both the fixed and the moving types. It showed among other things that, although a fixed flight simulator provided satisfactory results in most cases, there were certain ranges of control variables which could be studied in a simulator only if motion effects were included. The third report was Memo 3-6-59A, "The Use of Flight Simulators for Pilot-Control Problems," by George A. Rathert, Brent Y. Creer, and Joseph G. Douvillier, Jr. This report provided, for that time, a useful survey of the application and requirements of ground-based flight simulators.

Automatic Control. Lines of guidance and control research begun earlier were continued during this period. William Triplett and Stanley Schmidt were occupied with studies of control-system dynamics and Elwood Stewart and Gerald Smith were busy with the optimization of missile guidance systems. The latter work is covered in Memo 2-13-59A, "The Synthesis of Optimum Homing Guidance Systems."

 


[
291]

Pitch-roll chair.

Pitch-roll chair.

 


George A. Rathert.

George A. Rathert.

 

Landing Approach. The landing-approach studies commenced during an earlier period were also continued during 1958. One important result of this later work was Memo 10-6-58A, "A Flight Evaluation of the Factors Which Influence the "Selection of Landing Approach Speeds." This report, written by Ames test pilots Fred Drinkwater and George Cooper, discussed, from a pilot's point of view, the factors which influence the selection of landing approach speeds. In the end they recommended a certain "power approach technique designed to take some of the guesswork and variability out of the landing maneuver.

The rather extensive landing-approach studies made by the Ames Flight Research Section had indicated that the landing-approach maneuver could more easily be accomplished if a simple, reliable method were available for quickly controlling the thrust of jet engines. The thrust response of Jet engines was notably sluggish and when the pilot wanted a little more, or....

 


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292]

From left to right: Allan E. Faye, Donovan R. Heinle, and Glen W. Stinnett.

From left to right: Allan E. Faye, Donovan R. Heinle, and Glen W. Stinnett.

 

....a little less, thrust to change his approach-path angle, the desired thrust increment was not quickly obtainable. If, however, it were possible to leave the engine running at a good output and then to modulate the engine thrust by means of a fast-acting thrust reverser, the problem would he solved. The use of a thrust reverser after an airplane had touched down was generally accepted as feasible and desirable, but most aeronautical engineers shuddered at the thought of reversing the thrust of the engine while the airplane was still in the air. But this was exactly what Ames engineers proposed to do and did do. They built a thrust reverser, mounted it on a Lockheed F-94C fighter airplane and, after checking it out in the 40- by 80-foot tunnel, demonstrated its usefulness and safety in flight. This work attracted much attention in flight circles as it represented the first in-flight use of a jet thrust reverser. It was reported in Memo 4-26-59A (ref. B-61) by Seth Anderson, George Cooper, and Alan Faye.

 

BOUNDARY LAYER, SKIN FRICTION, AND AERODYNAMIC HEATING

 

For several years, Al Seiff had been exploiting to the fullest the unique capabilities of the supersonic free-flight (SSFF) tunnel. His conceptions were marked by originality and his technical and administrative leadership was of a very high quality. His staff, too, had been demonstrating great ability. On the covers of SSFF reports there were appearing with increasing [293] frequency the names of such people as Tom Canning, Simon Sommer, Barbara Short, and Carlton James. In the background supporting this research were of course numerous individuals whose contributions in such fields as instrument design, model building, facilities construction, and mathematical analysis were vital to the whole operation.

During 1958 the work of the SSFF group in the field of boundary layer, skin friction, and aerodynamic heating was represented by two reports, one of which was TN 4364 (ref. B-62) by Alvin Seiff and Barbara Short demonstrating the use of a Mach-Zehnder interferometer for boundary-layer work. The Mach-Zehnder interferometer was an extremely sensitive and somewhat fickle optical instrument, and its successful application to the precise measurement of boundary layers on models flying past at thousands of feet per second represented in itself a beautiful demonstration of experimental technique. Having mastered the technique, Al and Barbara were able to study the distribution of density gradients within the turbulent boundary layer and thereby to learn much about the heat-transfer characteristics of the boundary layer and the physical flow processes that take place within it.

The second SSFF project to be mentioned is one reported in Memo 10-9-58A, "An Investigation of Some Effects of Mach Number and Air Temperature on the Hypersonic Flow Over a Blunt Body," by Alvin Seiff and Simon C. Sommer. In this project, which was actually carried out in 1957 but was not reported until late in 1958, an attempt was made to separate the effects of Mach number and enthalpy on the pressures and temperatures in the flow around blunt bodies as well as on the forces and moments to which the bodies were subjected. In these tests a shock-compression light gas gun was used to obtain overall test Mach numbers of up to 15 and enthalpies of up to 2200 Btu/lb.

One of the more interesting boundary-layer studies made during 1957-1958 was conducted by Fred Matting, Dean Chapman, and Jack Nyholm and reported in TR R-82 (ref. B-63). These tests were particularly interesting because they represented the Laboratory's first major use of helium as a substitute for air in wind tunnels. Jackson Stalder had earlier used very small amounts of helium in his first low-density wind tunnel but, for this later application, quantities of helium were brought over in trailers from the Navy's helium storage facility at Moffett Field. This helium was used alternately with air in a special 1- by 10-inch blowdown tunnel, or channel, constructed within the building that housed the 1- by 3-foot tunnels. In this facility, direct measurements were made of the local skin friction in a turbulent boundary layer through a Mach-number range from 0.2 to 9.9 and a Reynolds-number range from 2 to 100 million.

Air was used as the working fluid at Mach numbers up to 4.2 and helium for the higher Mach numbers. The change to helium facilitated the attainment of high air-equivalent Mach numbers and at the higher test Speeds enabled the attainment of much higher Reynolds numbers. The [294] physical measurements made during the tests were correlated with theory and it was demonstrated that boundary-layer measurements obtained with helium could be interpreted in terms of measurements made in air. This correlation, however, would not be expected to hold if the boundary layer were intersected by strong shock waves.

The 10- by 14-Inch Tunnel Branch during 1958 remained active in the general field of aerothermodynamics. Fred Hansen and Steve Heims continued their useful studies of the properties of gases at high temperature, while Bernie Cunningham and Sam Kraus made the first practical use of a prototype shock tunnel which they, with the help of others, had recently completed. The work of Cunningham and Kraus was in the form of heat-transfer measurements made on a yawed cylinder representing the leading edge of a swept wing. This work, which seemed to demonstrate the potential value of shock tunnels, was reported in RM A58EI9.

 

BALLISTIC MISSILES AND SPACECRAFT

 

By early 1958, NACA had become engaged in the planning of a space research program. Its interests in this regard were reflected in the subject matter of the papers presented at the NACA Conference on High Speed Aerodynamics held at Ames in March. A major item in NACA's space research plans was the launching into orbit of a manned vehicle and the question arose as to what kind of a vehicle it should be. A number of possibilities existed. The vehicle could be a simple blunt-nose capsule like an ICBM warhead, having no lifting capability. It could also be a relatively simple capsule which by virtue of a nonsymmetrical shape and elementary control flaps would be capable of producing small amounts of lift (L/D from 0.5 to 1.0) for achieving a degree of reentry flight-path control. Or it could be a winged glider providing considerable control over its reentry path and landing site.

Each of these possibilities was explored in papers presented at the Ames Conference. In general, it appeared that Langley research men favored a nonlifting vehicle, and Ames research men, a lifting vehicle of some kind. Each had certain advantages. The lifting vehicle held out possibilities for controlling deceleration and heating, which were critical factors in a man-carrying device, and its ability to maneuver in landing was an obvious advantage. A prime advantage of the nonlifting body was the simplicity of its construction and operation. Also its weight, which would be less than that of a lifting vehicle, was more in line with the limited thrusting capacity of existing booster rockets. As long as the aerodynamic heating and decelerations were not beyond human endurance, the nonlifting vehicle, it appeared, should be very satisfactory. In this connection, Allen and Eggers had demonstrated how aerodynamic heating could be controlled through blunting, while Eggers, Allen, and Neice in TR 1382 had shown [295] that, for long ranges as well as for very short ranges, the decelerations to which a nonlifting vehicle would be subjected could be made humanly tolerable.

For the time being, at least, the virtues of the nonlifting vehicle seemed to outweigh those of the lifting vehicle. The dominating influence was perhaps competition. The Russians had convincingly demonstrated their satellite-launching capabilities as well as the impressive power of their booster rockets. They would not be long in putting a man into space. Also, the Air Force had initiated a man-in-space project and was moving ahead with it with all possible speed. It was clear that for NACA, as well as for the Nation, the watchword was speed. The vehicle that would allow the man-in-space task to be accomplished most quickly was the one to be chosen at this time. Later, other types of vehicles could be tried. The answer now seemed to be the simple, nonlifting vehicle.

The Ames Laboratory at this time became interested in orbits and trajectories. Material evidence of this interest appeared in the form of Memo 12-4-58A, "Three-Dimensional Orbits of Earth Satellites, Including Effects of Earth Oblateness and Atmospheric Rotation," by Jack N. Nielsen, Frederick K. Goodwin, and William A. Mersman. This was one of Nielsen's last projects before leaving NACA.

Another trajectory analysis, certainly one of Ames' most outstanding productions for the year, was made by Dean Chapman and published as TR R-11 (ref. B-(64), "An Approximate Analytical Method for Studying Entry into Planetary Atmospheres." This study, which again demonstrated Chapman's impressive research capabilities, shed a large amount of light on reentry problems and provided valuable analytical procedures for dealing with those problems. The blunt-body analysis made by Allen and Eggers and the performance study of long-range hypervelocity vehicles made by Eggers, Allen, and Neice had years earlier dealt in a somewhat limited way with certain vital aspects of the aerodynamic heating and reentry 2 problems. Chapman's analysis, however, was much broader; it encompassed the two earlier theories and provided more exact and versatile mathematical tools for dealing with reentry problems. It considered the special problems of entry into the atmospheres of other planets (Venus, Mars, Jupiter) as well as into that of Earth. It also considered a variety of lifting and nonlifting entry bodies or vehicles and several entry techniques.

[296] Chapman's study indicated that, during entry, the total heat absorbed by a spacecraft is less, and the deceleration it experiences is greater, as the entry angle relative to the local horizon increases. In the case of nonlifting vehicles, entry angles much above 3° produce decelerations beyond the limit of human endurance. Confirming earlier predictions by Eggers and Allen, Chapman found that a lifting vehicle entering the atmosphere at a moderate entry angle would tend to skip like a flat stone thrown at a millpond. While the total heat energy gained by the vehicle in this case would be less than for a nonskipping entry, the intensity of heating and deceleration at the bottom of the skips would, on the other hand, be particularly high and hard to cope with. It was thus becoming clear that returning spacecraft, particularly those of the nonlifting variety, would have to be guided into the Earth's atmosphere with considerable precision if safe and sure landings were to be accomplished.

One of the useful findings of Chapman's study was that only a small amount of lift was required in a satellite reentry vehicle to achieve a rather large amount of good. From a decaying circular orbit a vehicle developing a lift-drag ratio of only 0.5 would experience a much lower maximum deceleration and be subject to a much lower (about half) maximum heating rate than a nonlifting vehicle. It would, however, owing to longer flight times and lower average Reynolds numbers, absorb more heat. On balance, the advantage appeared to lie heavily with the lifting vehicle.

A spacecraft capable of producing an L/D of from 0.5 to 1.0 did not require wings. A body having the shape of a blunt cone, with the upper half removed, might do the trick, though some simple control flaps would probably be required to keep it flat side up and stable. Such a configuration had, indeed, been proposed by Al Eggers and investigations of the Eggers flattopped lifting bodies were now being undertaken in a number of Ames facilities.

One of the important reports resulting from these investigations was Memo 10-2-58A (ref. B 65), "Re-entry and Recovery of Near-Earth Satellites With Particular Attention to a Manned Vehicle," by Alfred J. Eggers and Thomas J. Wong. Since the lifting vehicles were expected to be controllable in landing as well as in reentry, their slow-speed characteristics were of much interest. Representative of the slow-speed tests run on such vehicles were those conducted in the 12-foot tunnel and reported in Memo 12-24-58A, "Subsonic Aerodynamic Characteristics of Several Blunt, Lifting, Atmospheric-Entry Shapes," by Howard F. Savage and Bruce E. Tinling.

Interest in the dynamic stability of ballistic-missile warheads, an interest which had originated in an earlier period, now extended to man-carrying reentry bodies having even more stringent stability requirements. Allen had earlier pointed out that a reentry body acquires a degree of apparent or [297] pseudo-dynamic stability by virtue of the fact that the density of the air it encounters in its descent is rapidly increasing. This benefit, which is a function of the rate of change of density with time, would tend to die out as the speed decreased and would then be overcome by any basic instability that the body might have. The degree of apparent stability, depending as it does on rate of descent, and thus on path angle, would obviously be less for a lifting manned vehicle.

Considerations of the kind just noted added to the interest in reentry dynamics that prevailed at this time and provided the instigation for a number of research projects. One of these, reported in TM X-20 by Barbara Short and Simon Sommer, was an investigation in the SSFF tunnel of the static and dynamic stability of two blunt-nose bodies through a range of angles of attack. Another project, of analytical character, was reported in Memo 3-2-59A, "Study of the Oscillatory Motions of Manned Vehicles Entering the Earth's Atmosphere," by Simon C. Sommer and Murray Tobak.

Late in 1958 the Ames Laboratory became actively interested in an airloads problem of unusual character. It concerned the airloads produced by the action of wind on large missiles of the ICBM type standing vertically on the launching pad. The wind produces a pulsating pattern of loads that must be considered not only in the structural design of the missile but also in the design of its guidance system. The pulsating aspects of the wind load arise from the unsteady processes represented by the formation and shedding of vortices in the wake. The phenomena involved were the same as had much earlier been encountered in wind flow around smokestacks, but the structure of a missile was necessarily much more fragile, and certainly more costly, than that of smokestacks. To investigate this problem, a dynamically scaled model of the Titan ballistic missile was installed in the 12-foot tunnel. The air loads, both static and dynamic, were measured, as were the effects of a model umbilical tower mounted adjacent to the missile model. The results of this study were reported by Don Buell and George Kenyon in

Before leaving NACA, Milton Van Dyke attacked one of the more difficult remaining problems in the field of aerodynamic theory. This was the problem of developing a convenient analytical procedure for determining the aerodynamic flow conditions that exist in the restricted zone between a blunt body and the bow shock wave it produces. This problem, known as the "blunt-body problem," had proved extremely resistant to theoretical treatment even when simplifying assumptions were made-assumptions that the properties of the air behind the shock wave remained constant and that the viscosity of the air was zero.

The blunt-body problem was the more difficult because of the existence of a mixed-flow region behind the shock wave. At the nose of the body is an occluded pocket of subsonic flow which becomes transonic and then super-[298] -sonic as the air accelerates around the curve of the body. The problem also involved the questions What was the shape of the shock wave produced by a blunt nose of a given configuration? And what was the standoff distance between the shock wave and the nose?

Van Dyke's study of the problem resulted in the development of a rapid numerical method, suitable for machine computation, for analyzing the flow around certain important classes of blunt body. The usual simplifying assumptions were made in Van Dyke's analysis, but these were by no means invalidating. The analysis dealt mainly with the subsonic region of flow, began with an assumed shape for the shock wave, and proceeded down stream to determine the nose shape that would produce such a shock wave. If the nose shape did not correspond to the one of interest, the process would be repeated until the desired nose shape was achieved. Repetitive numerical procedures of this kind had become feasible and attractive as a result of the fantastic operational speeds of electronic computers. Van Dyke's method was original in character, was timely and useful, and was amenable to improvement. First described in the Journal of the Aeronautical Sciences (ref. B-66), the method was demonstrated through a number of applications in the report TR R-1, "Supersonic Flow Past a Family of Blunt Axisymmetric Bodies," by Milton D. Van Dyke and Helen D. Gordon.

 


1 New NASA report designations to be described later.

2 There was some argument as to whether the term should be "reentry" or just plain entry.'' Purists held that a vehicle could not be said to have reentered the atmosphere if it had not made a prior entry or had not at least departed from the astronomical body in question. Both terms referred to the inward traversing of planetary atmospheres but in the most common case-that of a spacecraft returning to a planet (Earth) from which it had earlier departed- reentry'' seemed the more descriptive term and was more widely applied. Both, however, are Used in this work.


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